The present disclosure relates to an optical waveguide structure and an optical waveguide circuit.
A quadrature phase modulation method has been popular as a representative and practical coherent modulation method; Further, since a Dual Polarization Quadrature Phase Shift Keying (DP-QPSK) method using the quadrature phase modulation method in combination with a polarization multiplexing technique can increase frequency utilization efficiency, the DP-QPSK method is considered to be a more promising technique for realizing high capacity optical transmission.
As a demodulator of the DP-QPSK modulation method, there is known a configuration example realized by an optical waveguide circuit including elements integrated by using a Planar Lightwave Circuit (PLC) technique (see JP 5684131 B, for example).